|Database: Current Contents(tm) from ISI
Copyright 1992, 1995 Institute for Scientific Information, all rights reserved.
Chen, F.Z.; Judge, D.L.; Wu, C.Y.R.; Caldwell, J.
Low and room temperature photoabsorption cross sections of NH/sub 3/ in the UV region
Planetary and Space Science (Jan.-Feb. 1999), vol.47, no.1-2 p. 261-6.
Abstract: Using synchrotron radiation as a continuum light source, the authors have measured the absolute
absorption cross sections of NH/sub 3/ with a spectral bandwidth (FWHM) of 0.5 AA. The
photoabsorption cross sections of NH/sub 3/ have been measured from 1750 to 2250 AA under
temperature conditions of 295, 195, and 175 K. Significant temperature effects in the absorption
threshold region which are mainly due to the presence of hot band absorption are observed. The
cross section value at peaks and valleys for the vibrational progressions of the (0,0) to (4,0) bands
vary between -80% and +40% as the temperature of NH/sub 3/ changes from 295 to 175 K. In
contrast to this, the changes of cross section values, P/sub c,T/, are found to vary less than 20%
for the ( upsilon ', 0) vibrational progressions with upsilon '>or=5. The measured separations
between the doublet features of the (0,0), (1,0), and (2,0) bands are found to decrease as the
temperature of NH/sub 3/ decreases. The shifts of peak positions of P/sub c,T/ with respect to the
corresponding room temperature absorption peaks show a sudden change at upsilon '=3 which
appears to agree with the trend observed in the homogeneous line widths of the vibrational bands of
NH/sub 3/. The unusual behavior of the line widths has been attributed to the A state potential
surface which has a dissociation barrier.
Pub. Type: Journal Paper